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Resistor Design
About Resistors ( R ), are the most fundamental and commonly used of all the electronic components, to the point where they are almost taken for granted. There are many different Types of Resistors available such as: *Carbon (most common) *Film (Metal Film, Carbon Film and Metal Oxide Film) *Wirewound Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as Temperature Rating, Physical Size and Reliability. There are a large variety of fixed and variable resistor types with different construction styles available for each group, with each one having its own particular characteristics, advantages and disadvantages compared to the others. Carbon design Carbon Resistors are the most common type of Composition Resistors. Carbon resistors are a cheap general purpose resistor used in electrical and electronic circuits. Their resistive element is manufactured from a mixture of finely ground carbon dust or graphite (similar to pencil lead) and a non-conducting ceramic (clay) powder to bind it all together. The ratio of carbon dust to ceramic (conductor to insulator) determines the overall resistive value of the mixture and the higher the ratio of carbon, the lower the overall resistance. The mixture is molded into a cylindrical shape with metal wires or leads are attached to each end to provide the electrical connection as shown, before being coated with an outer insulating material and color coded markings to denote its resistive value. Tolerances Carbon composite resistors are generally prefixed with a "CR" notation (eg CR10kΩ ) and are available in E6 ( ±20% tolerance (accuracy) ), E12 ( ±10% tolerance) and E24 ( ±5% tolerance) packages with power ratings from 0.125 or 1/4 of a Watt up to 2 Watts. Carbon composite resistors are very cheap to make and are therefore commonly used in electrical circuits. Storr, Wayne., Types of Resistors. May 2011. http://www.electronics-tutorials.ws/resistor/res_1.html Film design A generic term "Film Resistor" consist of Metal Film, Carbon Film and Metal Oxide Film resistor types, which are generally made by depositing pure metals, such as nickel, or an oxide film, such as tin-oxide, onto an insulating ceramic rod or substrate. The resistive value of the resistor is controlled by increasing the desired thickness of the deposited film giving them the names of either "thick-film resistors" or "thin-film resistors". Once deposited, a laser is used to cut a high precision spiral helix groove type pattern into this film. The cutting of the film has the effect of increasing the conductive or resistive path, a bit like taking a long length of straight wire and forming it into a coil. This method of manufacture allows for much closer tolerance resistors (1% or less) as compared to the simpler carbon composition types. The tolerance of a resistor is the difference between the preferred value (i.e, 100 ohms) and its actual manufactured value i.e, 103.6 ohms, and is expressed as a percentage, for example 5%, 10% etc, and in our example the actual tolerance is 3.6%. Film type resistors also achieve a much higher maximum ohmic value compared to other types and values in excess of 10MΩ (10 Million Ω´s) are available. Film design Another type of resistor, called a Wire-wound Resistor, is made by winding a thin metal alloy wire (Nichrome- 60% nickel, 16% chromium, 24% iron per foot) or similar wire onto an insulating ceramic former in the form of a spiral helix similar to the film resistor above. These types of resistors are generally only available in very low ohmic high precision values (from 0.01 to 100kΩ) due to the gauge of the wire and number of turns possible on the former making them ideal for use in measuring circuits and Wheatstone Bridge type applications. They are also able to handle much higher electrical currents than other resistors of the same ohmic value with power ratings in excess of 300 Watts. These high power resistors are molded or pressed into an aluminum heat sink body with fins attached to increase their overall surface area to promote heat loss and cooling. These types of resistors are called "Chassis Mounted Resistors". They are designed to be physically mounted onto heat-sinks or metal plates to further dissipate the generated heat increasing their current carrying capabilities even further. References Links *Resistor Construction See also Resistors Video thumb|300px|right|MAKE presents: The Resistor Category:Electronics Category:Components